ZnO-Based Nanostructuring Strategy Using an Optimized Solution Process in CuInS₂ Superstrate Photovoltaics

Abstract

Nanostructuring strategies have received significant attention recently in the context of thin-film solar cell design. Superstrate-type CuInS 2 (CIS) thin-film solar cells based on hydrothermally grown ZnO nanorod (NR) arrays have been prepared through dimensional optimization and comparative parametric characterization to yield a highly efficient device configuration. Solution-processed transparent ZnO nanostructures covered with a uniform CdS buffer layer were prepared using liquid processing methods to achieve efficient light harvesting and transport of photogenerated charge carriers. Molecular precursor solutions containing metal and chalcogen precursors of CIS light absorbers yielded interpenetrated radial p−n junctions across nanostructured CdS/ZnO NR arrays. The performances of solar cells could be improved by experimentally optimizing device configurations across certain experimental parameters, such as the CIS annealing temperature, the buffer-layer thickness, or the NR length, all of which affect charge conduction and charge recombination kinetics. The interfacial charge-transfer properties and recombination characteristics were investigated by observing the dark current, electrochemical impedance, and open-circuit voltage (V oc ) decay. Impedance data were fit to a proposed equivalent circuit model consisting of resistor−capacitor (ZnO/CdS) and resistor−constant phase element (CPE) (CdS/CIS) components as a means for characterizing the interfacial properties. Recombination at the p−n interface increased in samples comprising a thin buffer layer and long NRs. A 250°C process temperature and optimal CdS deposition and ZnO NR growth times yielded the best efficiency, 6.8%. Our results suggest that solution-processed superstrate structures prepared using nanostructuring approaches could provide highly efficient low-cost photovoltaic devices.

Solution-processed solar cells based on inorganic bulk heterojunctions with evident hole contribution to photocurrent generation

“…4 Due to their nontoxicity, stability to environment, transparency to visible light, high electron mobility and ready availability by solution reactions, vertically aligned nanorod/nanowire arrays (NAs) of ZnO 5 and TiO 2 6 have been widely used as the ideal electron acceptor and transporter in devices such as dye-sensitized solar cells (DSCs) and hybrid polymer-based solar cells (HPSCs). 10,14 Recently, Lee and Yong 15 filled the molecular precursors for CuInS 2 into the CdS nanocrystal coated ZnO-NA and prepared the solar cells after the CuInS 2 nanocrystal had formed inside the ZnO-NA by thermal decomposition of the precursor molecules. [7][8][9][10] However, the ISCs from preformed nanocrystals often encounter deficiencies related to their small size, such as high exciton binding energy, 11 low carrier concentration and high trap density, 12 charge conduction level dispersion and grain boundary issues (e.g.…”

Efficiency Improvements in Solution‐Based CuInS2 Solar Cells Incorporating a Cl‐Doped ZnO Nanopillars Array

“…At the same time, ZnO has also been extensively employed as n‐type semiconductor or window layer both in inorganic and hybrid solar cells . Although these materials are mainly prepared using high vacuum techniques, solar cells built with solution‐based methods that combine chalcopyrites and ZnO are not uncommon, and their efficiency has been increasing steadily over the last years . Various deposition methodologies have been used, such as electrodeposition, spraying and solution growth techniques .…”

“…[3,4] Although these materials are mainly prepared using high vacuum techniques, solar cells built with solutionbased methods that combine chalcopyrites and ZnO are not uncommon, and their efficiency has been increasing steadily over the last years. [5][6][7][8][9][10][11][12][13][14][15][16] Various deposition methodologies have been used, such as electrodeposition, [5,11] spraying [12][13][14] and solution growth techniques. [10] However, many of these cells are prepared in substrate configuration and involve a layer of toxic CdS or a stage involving hazardous hidrazine or require a thermal treatment in highly toxic H 2 S atmosphere.…”

Three dimensional web-like fibrous CuInS2 film

“…Three-dimensional structures for solution-processed CIS solar cells have been designed [12][13][14][15] using hydrothermally-grown ZnO and sputtered ITO nanorod arrays as illustrated in Fig. 1.…”